1. Field of the Invention
The present invention generally relates to semiconductor integrated circuit devices, and more particularly to a semiconductor integrated circuit device that operates in synchronism with an external clock signal applied thereto.
2. Description of the Related Art
Recently, semiconductor integrated circuit devices have been required to operate at higher frequencies. For example, memories are required to operate at higher speeds as CPU operates faster. For example, SDRAM (Synchronous Dynamic Random Access Memory) and DDR-SDRAM (Double Data Rate SDRAM) can operate at a high frequency in synchronism with an external clock signal applied therefrom. Such memories must be equipped with a high-speed, high-precision input circuit supplied with a clock signal and a data signal from the outside of the memories.